1. Field of the Invention
The present invention relates to devices and methods for monitoring biopotentials. More particularly, but without limitation, the present invention relates to a method and device for monitoring or sensing a biopotential and wirelessly transmitting the monitored condition.
2. Problems in the Art
Biopotential sensors are known in the art. In a conventional arrangement, such as with electrocardiograph (ECG) leads, the sensors/leads are connected to a bedside monitor through wires. The bedside monitor may also be wired to a nursing station or other central station for monitoring purposes. Thus there are two locations at which a patient""s physiological condition needs to be monitored: (1) at the location of the patient and (2) at a nursing station or central station.
The use of wires to make these connections may create problems. For example, at times a patient connected to an ECG or other sensors may need to be moved very quickly to a different part of a hospital. In this scenario, the electrodes must either be removed from the patient or the monitor must be moved with the patient. Removing the electrodes or other sensors from the patient requires additional time. Later reconnecting the electrodes or sensors requires additional time as well. Other problems are introduced by the detachment of the electrodes as well, including additional patient discomfort as well as damage to the electrodes or weakening of the electrode interface. Thus there is a need in the art for a biopotential sensing device and method which minimizes the use of wire connections between a patient and a central station.
In some prior art devices, a portable monitoring device may be used that wirelessly transmits physiological information to a nursing station or central station. This eliminates some of the problems associated with wiring, in that the portable monitor may remain wired to a patient. However, problems remain, in that the wires between the patient""s sensors and the portable monitoring device may still need to be detached in order to provide medical care to the patient. Thus there is a need for a medical monitoring system that minimizes the connections between a patient and a monitoring device.
Another prior art approach has involved the use of a sensor coupled with a transmitter, in order to remove the need for wires between the sensor and monitoring equipment. One example of this type of device is disclosed in U.S. Pat. No. 5,634,468, entitled Sensor Patch and System for Physiological Monitoring, issuing on Jun. 3, 1997. The prior art device provides for wireless transmission from a sensor to a receiver located on a patient and for communication via a standard telephone network from the receiver. Thus the problem of eliminating wires between a patient unit and a central monitoring station remain and other problems are introduced that are consistent with other problems of using wireless systems within a hospital environment.
One of these problems involves electromagnetic radiation. The medical and scientific community are beginning to realize the harmful effects that exposure to electromagnetic radiation can have on the human body and its vital organs. Any placement of a transmitter on the human body creates concerns regarding electromagnetic radiation exposure. This is particularly true with medical monitoring systems due to the proximity of the transmitter and the continuous operation of the device.
Another problem is electromagnetic interference. Electromagnetic interference affects the integrity of wireless systems, a problem which is acutely troublesome in critical care applications where if a system fails or otherwise improperly functions, a person may not receive medical care when needed. Increasing the number of wireless devices adds to the problem instead of addressing it or eliminating it. In a hospital setting, various other problems serve to compound the problem. One such problem is the current limitations on the amount of allocated frequency space for medical applications. Although spectral resources have been allocated for wireless telemetry medical services, this allocation is limited. Other available frequencies may share with other users, making these frequencies less suitable for critical care applications.
This limited availability of allocated frequencies further increases the likelihood that interference may occur within a hospital. Prior solutions have attempted to avoid the problem by making equipment operate at multiple frequencies. For example, in U.S. Pat. No. 5,458,123, entitled System for Monitoring Patient Location and Data, issuing on Oct. 17, 1995, a different carrier frequency is allocated to each patient.
Having equipment operate at user-selectable frequencies is simply a poor solution in critical care applications. This type of methodology is only useful where a particular electromagnetic interference problem has already been identified. For example, if two wireless patient monitors are operating in the same room, then it should be known that they should not be operating at the same frequency or else interference may result. Unfortunately, one does not always know when different frequencies should be selected, as electromagnetic interference is not generally so predictable. In some facilities the number of frequencies available may be smaller than the number of patients that need to be monitored, thus that two or more patients may be operating on the same frequency. Furthermore, manufacturing a device that can operate on so many different frequencies can dramatically increase the cost and size of the device. In addition, although operation on the same frequency may ensure interference, selection of different frequencies does not eliminate the possibility of electromagnetic interference.
Spread spectrum communications is another solution to electromagnetic interference that has been used in medical devices as well as various other industries. For example, in U.S. Pat. No. 5,381,798, entitled Spread Spectrum Telemetry of Physiological Signals, issuing on Jan. 17, 1995, a spread spectrum transmitter and a spread spectrum receiver are used to transmit ECG information. In spread spectrum communications, bandwidth is sacrificed in order to increase signal-to-noise ratios. An increased signal-to-noise ratio makes a device less susceptible to noise-type interference. Thus spread spectrum systems do have certain advantages, however, as more and more devices are used on the same frequencies, these advantages continue to decrease and there is a further need for bandwidth. Furthermore, increased transmission power may be required because the transmission is over a wider band. The increased transmission power is related to increased likelihood of interference and shortens battery life in a battery-operated transmitter. Thus many deficiencies in the prior art remain.
The present invention includes a new wireless biopotential monitoring system which has the advantages of limiting electromagnetic interference. The biopotential monitoring system includes a sensor unit having a transmitter. The sensor unit may include an external auditory canal temperature sensor according to the present invention, an earpiece pulse oximeter according to the present invention, or an ECG or other sensor. The biopotential monitoring system may also include a patient monitor for monitoring biopotentials and physiological conditions at or near the patient. The monitoring system may also include a monitor located at nursing station or central location. The transmitter in the sensor unit is adapted for low power transmissions.
The present invention also includes a method of medical monitoring that permits biosensors to sense physiological data and wirelessly transmit the physiological information from a plurality of sensors to a patient unit. The patient unit then interleaves the physiological information at the patient unit and wirelessly transmits the interleaved information to a monitor unit.